Switches for high frequency waves



April 5, 1955 A, T. STARR ETAL SWITCHES FOR HIGH FREQUENCY WAVES 5Sheets-Sheet 1 Filed Feb. 4, 1952 A tl rne y April 5, 1955 A. T. STARRETAL 2,705,776

SWITCHES FOR HIGH FREQUENCY WAVES Filed Feb. 4, 1952 3 Sheets-Sheet 2 Inventor A .TI 5 'ARR GnKM/G By- W Attorney April 5, 1955 A, T. STARREl'AL SWITCHES FOR HIGH FREQUENCY WAVES 5 Sheets-Sheet 3 Filed Feb. 4,1952 FIGS.

A itorney United States Patent SWITCHES FOR HIGH FREQUENCY WAVES ArthurT. Starr and George King, London, England, as-

signors to International Standard Electric Corporation, New York, N. Y.

Application February 4, 1952, Serial No. 269,872

Claims. (Cl. 333-7) The present invention relates to switch devices forelectro-magnetic wave guides.

In high frequency radio systems employing waveguides it is frequentlyrequired to carry out switching operations whereby one waveguide can beconnected to either of two or more others. The mechanical requirementsof a waveguide switch are quite simple, but is found that considerableditficulties are encountered in meeting the electrical requirements.

The problem in the case of a waveguide switch is to provide paths forthe high frequency energy between members of the switch having relativemovement. It is well known to provide spring leaves, or similar devices,for making contact between fixed and moving members of a high frequencytransmission device. In the case of a switch, this solution is difficultto realise in practice in such manner that absolutely reliable contactis obtained over a long period of operation. The solution according tothe present invention depends on an alternative principle by which theelements of the switch are proportioned so that satisfactory paths forthe high frequency energy are produced without mechanical contactbetween fixed and moving parts of the switch.

A switch of this kind must involve clearance gaps which produceundesired cross-couplings, and introduce irregularities into thewaveguide which are the cause of reflections and loss. It is thereforenecessary to design the mechanical details in such manner as to minimiseor eliminate the irregularities and cross-couplings produced by theswitch.

A large number of different forms of waveguide switch have been proposedin the past, and the form chosen for the present invention is generallysimilar to a well known form of gas tap. The invention consists in themeans adopted for overcoming the electrical difliculties of a switch ofthis kind.

The invention accordingly provides an electro-magnetic waveguide switchcomprising a hollow metal body having a cylindrical cavity therein, atleast three waveguide sections communicating with the cavity, acylindrical metal drum coaxially and rotatably mounted inside thecavity, with a small cylindrical clearance gap between the inner wall ofthe cavity and the outer wall of the drum, the drum also carrying awaveguide passage so disposed as to connect together one pair of thesaid waveguide sections when the drum is switched to one given position,and to connect a different pair when the drum is rotated to a dilferentgiven postiion, and a plurality of radial quarterwave slotscommunicating with the said clearance gap and located in such manner assubstantially to prevent electromagnetic waves which are passing throughthe waveguide passage from leaking through the said clearance gap.

The invention will be described with reference to the accompanyingdrawings, in which:

Fig. 1 shows a top view of a waveguide switch according to theinvention, with a small portion broken away to show a detail.

Fig. 2 shows a sectional view at AA of Fig. 1;

Figs. 3 and 4 show details of the drum portion of the switch, Fig. 4being a front elevation, and Fig. 3 being a section at B-B of Fig. 4;

Fig. 5 shows a diagrammatic sectional view of the switch showing amodified form of drum; and

Fig. 6 shows a section of another modification of the drum.

Referring to Fig. 1, the switch comprises a hollow cylindrical metalbody 1 from which radiate four short secice tions 2, 3,4, 5 ofrectangular waveguide terminating in flanges to which other lengths ofwaveguide (not shown) may be bolted. Inside the cylindrical body islocated a rotatable metal drum 6, through which run two similar bentpassages 7, 8 having the same cross-section as the waveguide sections.These passages are seen in the section of the drum shown in Fig. 3. Theexternal openings of these passages are spaced apart by round thecircumference of the drum. The drum rotates in bearings 9, 10 carried bythe upper and lower cover plates 11, 12 of the body of the switch.

The drum carries a radial cylindrical hole 13 (Fig. 4), in which arehoused a ball 14 and a spring 15 (Fig. 1) which act in conjunction withfour equally spaced holes 16 (Fig. 1) in the cylindrical body 1 to forma click mechanism for locating the operated positions of the drum. Thearrangement is such that in two diametrically opposite positions of thedrum, the guide sections 2 and 4 are respectively connected to guidesections 3 and 5 through the passages 7 and 8, while in the other twodiametrically opposite positions a quarter of a turn from the formerposition, the guide sections 2 and 4 are respectively connected to theguide sections 5 and 3.

It will be appreciated that a cylindrical gap of appreciable dimensionsmust exist in practice between the outer surface of the drum 6 and theinner surface of the body 1. it is found that even with the-smallestpracticable gap, excessive leakage of the electro-magnetic waves betweenthe two pairs of guide sections which are separately connected by thepassages 7 and 8 always occurs. This not only produces unwantedcross-couplings, but also a power loss, and an impedance irregularityproducing reflections.

According to the invention, the leakage is substantially prevented bycutting two radial slots 17 and 18 (Fig. 3) in the drum, bisecting theangles between the two passages 7, 8. One of these slots is visible inFig. 2, and also in Fig. 4. The depth of each slot should be equal toone quarter of the wavelength corresponding to the mean frequency of theband over which the switch will be used. Also it is preferable toproportion the diameter of the drum so that the circumferential distancebetween each wall of the slot and the adjacent Wall of the neighbouringpassage is one quarter of the same wavelength.

At the same time the surface of the drum should preferably be undercutby a few thousandths of an inch over a length equal to the longerdimension of the guide, as indicated at 19 in Fig. 4, where the undercuthas been exaggerated for clearness.

The rim portions 20, 21 of the drum should be designed to fit theinternal surface of the body 1 with the smallest practicable clearance,and they should be lubricated with a good electrically conducting greasecontaining graphite, for example. The rim portions 20 and 21 then formthe real bearings of the drum, and accordingly the axial bearings 9, 10should be provided with sufiicient clearance to permit free movement.

The conducting grease substantially seals the gaps between the rimportions 20, 21 and the body, and it will be appreciated that thepassages 7 and 8 will be connected at both ends round the circumferenceof the drum by a very narrow half-wave slot having a quarter wave slottapped off the centre. The effect is substantially to short-circuit thegaps between the drum and the body along the longer internal dimensionsof the waveguide, thus preventing any appreciable leakage of theelectromagnetic waves.

The bend at the centre of each of the passages 7 and 8 should, ofcourse, be proportioned according to known practice in order to obtainthe best voltage standing wave ratio at the midband frequency.

Fig. 5 shows diagrammatically a modification of the switch according tothe invention. In this case, a definite clearance of perhaps 0.005 inchis provided between the drum and the inside of the body 1 for the wholelength of the drum, and the axial bearings 9 and 10 will then be thereal bearings, and may, for example include ball or roller bearings.Leakage through the clearance in an axial direction is prevented bymeans of two coaxial circular slots 22 and 23 formed between the drum 6and two coaxial metal discs 24 and 25 of the same diameter as the drum,by means of two coaxial metal spacing discs 26 and 27 of such smallerdiameter than the drum that the radial depth of the circular slots soformed is a quarter wavelength at the midband frequency.

Fig. 6 shows a modification to Fig. 3 to indicate that by increasing theexternal diameter of the drum, and the internal diameter of the bodyaccordingly, two pairs of slots for suppressing the leakage of the wavesmay be provided.

The drum 28 is provided with two passages 29 and 30 similar to 7 and 8of Fig. 3 except that the straight portions are longer. Between thelower open ends of these passages are provided two quarter-wave slots31, 32, similar to 17 (Fig. 3), and arranged to divide the portion ofthe circumference of the drum between the passages into three equalparts, the diameter of the drum 28 being chosen so that the distanceseparating each of the slots from the other, and from the neighbouringpassage, is a quarter of the midband wavelengths.

Likewise two other similar and similarly arranged quarter-wave slots 33and 34 are provided between the upper mouths of the passages 29 and 30.

Fig. 6 also indicates an alternative method of arranging the clickmechanism. A cylindrical hole 35 parallel to the axis of the drum isprovided near the edge for housing a ball and spring (not shown)arranged like 14 and 15 (Fig. 1). These will co-operate with fourequally spaced depressions or holes in the top or bottom plate (notshown) of the body (also not shown).

The drum 28 in Fig. 6 can be designed as regards other features in asimilar manner to the drum 6 shown in Figs. 3 and 4.

It will be noted from Fig. 3 that leakage may occur round thecircumference of the drum from the input to the output end of the samepassage 7 or 8. This may not be of any importance, but it could easilybe suppressed if desired, by providing two additional quarterwave slots(not shown) similar to 17 and 18, and spaced 90 therefrom.

It should also be pointed out that if a simple change over switch isrequired, the guide section 5 (Fig. l) and the passage 8 (Fig. 3) mightbe omitted. Then the switch can be used to connect guide section 3 tosection 2 or 4 according to the position of the drum. Leakage into theunconnected guide section will then be prevented by the slots 17 and 18as already explained. In such a case the angle between the guidesections 2 and 3, and 2 and 4. need not be 90, provided that the singlepassage 7 is designed accordingly. The slots 17 and 18 should berespectively placed one quarter wave length circumferentially from theopen ends of the passages.

Various other connections could evidently be arranged on similar lines,and there could be more than four waveguide sections attached to thebody, and more than two passages in the drum. The principle to beadopted is to locate a radial quarter-wave slot in the path of theleakage to be suppressed, such slot being preferably a quarterwave-length circumferentially from the nearest open end of a passage.

While the principles of the invention have been described above inconnection with specific embodiments and particular modificationsthereof, it is to be clearly understood that this description is madeonly by way of example and not as a limitation on the scope of theinvention.

What we claim is:

l. An electromagnetic waveguide switch comprising a hollow metal bodyhaving a cylindrical cavity therein, at least four waveguide sectionsarranged symmetrically around the body and communicating with thecavity, a cylindrical metal drum coaxially and rotatably mounted in- Illside the cavity, with a small cylindrical clearance gap between theinner wall of the cavity and the outer wall of the drum, said drumcarrying a plurality 'of separate waveguide passages disposed so thatwhen the drum is rotated to a given position, each passage connectstogether a corresponding pair of the waveguide sections, and when thedrum is rotated to a different position, each passage connects togethera different pair of waveguide sections and two diametrically oppositeradial quarter-wave slots cut in said drum, the open end of each slotbeing arranged at equal circumferential distances from an adjacent openend of each passage, and the diameter of the drum being so proportionedthat the said circumferential distance is substantially a quarterwavelength 2. A switch according to claim 1 in which the drum comprisestwo n'm portions at opposite ends thereof enclosing therebetween acentral portion of diameter slightly smaller than that of the rims, thediameter of the said rims being such as closely to fit the internaldiameter of the cavity.

3. A switch according to claim 1 in which the drum and cavity are eachof uniform diameter throughout, comprising two circular coaxialquarter-wave slots arranged respectively at each end of the drum forsuppressing leakage of electromagnetic waves in an axial directionthrough the clearance gap.

4. An electromagnetic waveguide switch comprising a hollow metal bodyhaving a cylindrical cavity therein, four waveguide sections arrangedsymmetrically around the body and communicating with a cavity, a metaldrum coaxially and rotatably mounted inside the cavity, with a smallclearance gap between the inner wall of the cavity and the outer wall ofthe drum, said drum carrying two separate similar waveguide passagesdisposed in such manner that when the drum is rotated to a givenposition each passage connects together a corresponding pair of adjacentwaveguide sections, and when the drum is rotated through from the givenposition each passage connects together a diflFerent pair of adjacentwaveguide sections, at least two radial quarter wave slots,diametrically opposite to one another, carried by the drum andcommunicating with the clearance gap, each portion of the clearance gapwhich directly connects two open ends of different ones of saidpassageways being an integral number of quarter-wavelengths long, saidportions being divided circumferentially into an integral number ofquarter wave-length sections by radial quarter-wave slots which openinto said portions, whereby the electromagnetic waves are prevented frompassing from one passage into the other through the clearance gap.

5. A switch according to claim 4 comprising two diametrically oppositepairs of slots, the open ends of each pair of slots being arranged todivide the circumferential distance between two adjacent open ends ofdifferent passages into three equal parts, each of which parts issubstantially equal to a quarter wavelength.

References Cited in the file of this patent UNITED STATES PATENTS2,446,863 Yevick Aug. 10, 1948 2,454,761 Barrow et al Nov. 30, 19482,475,647 Spriggs July 12, 1949 2,573,713 Kannenberg Nov. 6, 2,599,314Bobb June 3, 1952 2,629,048 Dyke Feb. 17, 1953 OTHER REFERENCES Long, AHigh Speed K-Band Switch, Proceedings of the I. R. E., publishedDecember 1951, pp. 1566-67.

